Our invention is directed to an improved suture ring for a prosthetic heart valve and to a method and apparatus for securing the suture ring to the heart valve.
Mechanical artificial heart valves for humans are frequently fabricated from carbon and coated with another form of carbon known commercially as Pyrolite.TM., a trademark of Carbomedics, Inc., the assignee of our present invention. Pyrolitic carbon is employed because of its unusual nonthrombogenic properties. Human blood does not readily coagulate on contact with it. Moreover, it is lightweight, hard and quite strong.
A standard implantable mechanical heart valve usually has an annular valve housing or body to provide a passageway for blood. Occluders are mounted in the annular body and open or close the blood flow passageway. Usually there are one or two occluders, but occasionally triple occluder configurations have been proposed. On the outside of the valve body there is usually an external, circumferential surface configured as a groove. The purpose of this groove is to facilitate attachment of a suture ring to the valve body.
The suture ring is used to sew the heart valve to the patient's heart tissue. The ring generally comprises a knit fabric tube which is rolled into a toroidal form and which is secured about the heart valve body in the circumferential groove. Various methods and apparatus have been proposed for securing the suture ring to the heart valve. It is known, for instance, to bind the ring into the groove with a plastic thread. It has also been proposed to form a rotatable suture on the heart valve using heat shrinkable plastic material, as disclosed in U.S. Pat. No. 3,781,969. U.S. Pat. No. 3,491,376 suggests that a suture ring should be formed as a separate sub-assembly which should then be attached to the heart valve. In the '376 patent, the suture ring is described as including a resilient annular member which is temporarily deformed, so as to snap onto the valve body. U.S. Pat. No. 3,579,642 proposes the use of metal snap rings which must be radially expanded to place the suture ring about the valve body. In such fabrication techniques, however, there is a risk of potential damage to the suture rings when the ring is mechanically expanded to place it about the valve body.
In U.S. Pat. No. 4,743,253, Magladry proposed a two-part suture ring comprising the knit fabric and an internal crescent-shaped ring which would be deformed inwardly by electromagnetic forming to clamp the heart valve while permitting relative rotation between the suture ring and the heart valve.
Despite these efforts, there remains a need for improved techniques for attaching the relatively flexible knit fabric of the suture ring to the rigid, sometimes brittle material of the mechanical heart valve and for reinforcing the heart valve.